What you are feeding her sounds just fine to me. Make sure she does not get too fat. That will hurt fertility. If she starts to look chunky cut back or even eliminate the grain.
Something else did occur to me though. While I raised full sized dairy goats for years, I am not all that familiar with minis. Dairy goats, particularly the Swiss breeds (the ones with the upright ears) are seasonal breeders. The usual breeding season is from about September through February. I have on occasion had does come into heat as early as August and some can be bred as late as March. I have no idea if this applies to Nigerians or not, but I thought it was something to be aware of. Check with an experienced Nigerian breeder. The worst that can happen is that your doeling gets bred next fall rather than next spring.
She gets a little chubby when I put fresh hay in but slims back down when he stomach is empty.
I am on a fb page for Nigerians and hear that they go in heat in the fall (around august and september )and then in the spring (around march or april). Her being so young and the fact that she is half pygmy I am pretty sure she went into heat for the first time a few weeks ago. She will be a year in April and the other week she was swollen and I think I saw some red discharge and was flagging her tail a little.